June 22, 2009 -- Sharks may only kill for food, but they share similar strategies with human serial killers: They lurk out of sight, stalking their victims.
SLIDE SHOW: Great White Sharks Attack
Sharks and human serial killers can both be tracked using geographic profiling, according to a new study that applied this investigative technique to the hunting patterns of great white sharks, the world's largest known predatory fish.
The study, published in the latest Journal of Zoology, marks the first time geographic profiling has ever been used on a marine species.
"As predators, they must get close enough to check out prey and figure out their movements, but they also must be far enough way so that they themselves won't be easily tracked," co-author Neil Hammerschlag told Discovery News.
"They must use known traveling routes," added Hammerschlag, a University of Miami researcher in the Rosenstiel School of Marine and Atmospheric Sciences. "For human killers, these would be things like subways, buses and freeways. For great whites, these would include channels, reef edges and other topographical features."
For the study, Hammerschlag worked with shark expert Aidan Martin and former Canadian beat cop Kim Rossmo, who developed the geographic profiling technique and is now at Texas State University.
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The researchers observed and recorded 340 great white shark attacks on Cape fur seals in the waters off of Seal Island in South Africa's False Bay. They plotted these attack sites, using a radar chart to examine the distribution of the encounters and noting where the sharks began and ended their attacks.
All else being equal, attack frequency should be directly related to prey density, with sharks lurking where the most seals gather. Surprisingly, that wasn't the case.
The scientists determined sharks instead positioned themselves about 328 feet from the island at a water depth of around 82 feet. Hammerschlag thinks this might provide the optimal balance of being close enough for attack, yet not close enough for detection. A deep water starting point permits momentum, "allowing the shark to build up enough speed to initiate the attack."
The researchers also found that big adult sharks had very focused anchor points from which they repeatedly launched their offensives. Smaller, younger sharks were less focused.
"This could be because sharks learn to refine their hunting skills over time and know the best spots, or they could dominate smaller sharks and exclude them from the best areas," Hammerschlag explained, adding that cleverness at all attack stages is critical, since seals can do serious damage to sharks.
"A seal can rip a shark's eyes out and they have a lot of bacteria in their mouths that can cause infections when they bite," he said. "Many sharks have face gashes caused by seals."
Nevertheless, it's a shark-eat-seal world, and top predators like sharks play an important role in structuring communities and maintaining ecosystem health. The new findings help to solve mysteries about great white hunting behavior and can help to identify areas for protection -- of both humans and sharks.
"I wouldn't recommend holding a swim meet in known shark attack areas," Hammerschlag deadpanned, adding that boating, oil drilling and other human marine activities should be moved away from the regions for the sake of human and shark safety.
Steven Le Comber, an expert on geographic profiling at the School of Biological and Chemical Sciences at Queen Mary, University of London, believes the investigative technique "is an interesting way to study patterns of animal foraging, and especially predation."
He concluded, "Shark hunting patterns are extremely difficult to study and the work here will have important implications for our understanding of the ways in which predators hunt their prey."
Related Links:
Discovery News Blog: Born Animal
TreeHugger: 10 Tips for Avoiding Shark Attack
School of Biological and Chemical Sciences at Queen Mary
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